Section Two: Sun Shadow Volume Analysis

Introduction

Section Two: Sun Shadow Volume Analysis

Introduction

Shadow analysis is a tool that allows you to analyze daylight conditions by giving a certain date and time. It can be hourly analysis between sunrise and sunset or the changes in shadows at a certain time during different dates. It is a useful tool for building design and understanding the sun’s path in a given coordinate. Assume that you are a designer and you would like to design a high-performance building that its source of energy is solar. Also, the sun position and movement across your site play an important role in your design to benefit from the daylighting.

The most important questions would be how much does a building shade the surrounding area and how much does the surrounding area, such as buildings and trees, shade a building? It is obvious that trees’ shadows are desirable in summer and very important in cooling the environment, whereas in the winter the important factor in the environment is the shade created by buildings.

In this section, you will carry out the sun shadow analysis from sunrise to sunset in winter (January 1st, 2021). If you are interested you can carry out another analysis for summer (July 1st, 2021) to compare the results. Creating the shadow volumes, you will learn how to animate the shadow volumes that you have created.

2.1 Understanding 3D Features

Open UniversityParkCampus_Lesson6 Project in ArcGIS Pro.
Click the Project tab. Select Save As.

Credit: 2016 ArcGIS
In the Projects Folder (C:\Users\YOURUSER\Documents\ArcGIS\Projects\ UniversityParkCampus), Save Project as UniversityParkCampus_Lesson6_Shadow.
Go back to the Map view.
Make sure the following layers are checked in the 3D Layers Content Pane: Up_Roof_Segments, Building_Footprints., and Topography.

Note: What you have created in Lesson 5 as a 3D building, is an extrusion from attribute. It means that you extruded a 2D polygon based on a ‘Z’ attribute you extracted from LiDAR Data or DSM or any other sources. Having an extruded building, does not make your features with 3D geometry. It is just a 3D visualization of your 2D data. For many 3D spatial Analysis, you need 3D features or Multipatch features.

3D features are features with 3D geometry. 3D features can be displayed without the need to draping them over a surface like DEM. They already have Z information in their geometry. In the image below you can see how 2D features (Crème color) are dependent on a surface for display in a 3D scene, whereas 3D features (Red color) have z information and are located in the elevation they belong to without extrusion.

Credit: ChoroPhronesis Lab

Multipatch features are 3D objects that represent a collection of patches to present boundary (or outer surface) of a 3D feature. Multipatches can be 3D surfaces or 3D solids (volumes).

Different types of multipatch features.

Credit: ArcGIS [1]

Also, the icon next to a multipatch feature is a 3D feature. The image below shows the multipatch icon. For now the only supported type of features for multipatch layers are polygons. Points and lines can be converted to 3D features but not multipatch features.

Credit: 2016 ArcGIS
For ‘Sun Shadow Analysis’ you need multipatch features. Multipatch features for buildings are provided in Lesson6.gdb.
On the top ribbon, click Map and select Add Data. Locate Lesson6.gdb and select ‘Building_MP_Campus’.

Note: The reason that you will work on the smaller part of campus for this 3D spatial analysis is that your computer might not be able to handle bigger data. The multipatch layer for bigger areas of campus are also provided, in case you would like to carry on more analysis in your free time (Buildings_MP).
Right click on the symbol under layers to modify the color. Change the ‘Building_MP _Campus’ to Fire Red.

Credit: 2016 ArcGIS
Right-click on Building_MP_Campus and select Properties. Select Elevation from the menu. Set the features are, Relative to the ground. Click Ok.

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Uncheck UP_Roof_Segments. Now you can see what the multipatch surfaces look like. Navigate by holding down the scroll wheel or the V key and drag the pointer to tilt and rotate the scene.

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Test Your Knowledge
Uncheck this layer and check back the UP_Roof_Segments.

2.2 Sun Shadow Volume Analysis for January 1st

⁴ ArcGIS Pro [2]

⁵ ArcGIS Pro [2]

On the top ribbon, click the Analysis tab and select tools. Search Sun Shadow.
Select Sun Shadow Volume (3D Analyst Tools).

Credit: ArcGIS, 2021
You will use the multipoint feature ‘Building_MP_Campus’ as an input. On January 1st, 2021 the sunrise is at 7:54 am and sunset is 5:52 pm. Set the start and end date as below. Pennsylvania is in the Eastern Standard Time zone. Change the Iteration Interval to 2 and Iteration Unit to Hours. Click Run.

Credit: ArcGIS, 2021
Turn on UP_Roof_Segment and turn off Building_Mp_Campus. Change the color of SunShadow_January to ‘Topaz Sand’. Right-click on the layer, select Properties. Click Elevation and make sure the features are relative to the ground. This is the result of your analysis.

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Open the attribute table and you will see the fields that are attributed. The fields are explained in detail on the ArcGIS Pro website. Here is the explanation for each field:
- SOURCE—Name of the feature class casting the shadow volume.
- SOURCE_ID—Unique ID of the feature casting the shadow volume.
- DATE_TIME—Local date and time used to calculate sun position.
- AZIMUTH—Angle in degrees between true north and the perpendicular projection of the sun's relative position down to the earth's horizon. Values range from 0 to 360.
- VERT_ANGLE—Angle in degrees between the earth's horizon and the sun's relative position where the horizon defines 0 degrees and 90 degrees is directly above.⁴
Close the attribute table.
To make sense of the results of the shadow volumes, you need to symbolize the layer based on the time of day (every 2 hours position of the sun in the local date). On the content pane, click on the symbology under SunShadow_January1.
On the top ribbon, under appearance, click Symbology. Select Unique Values.

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On Symbology pane on the right side of ArcGIS Pro, select DATE_TIME as Value field.
Select set 3 for the color scheme.

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On the content pane or in the symbology pane you can explore the categories.

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The first category is the shadow created by the sun at 7:54 am and the last one is the shadow created at 3:54 pm. Because of the overlaying layers, you cannot see each shadow clearly.
On the top ribbon, click appearance. In Effects Category, define Layer Transparency as 30%.

Credit: ArcGIS, 2021

Making a Layer transparent, you can see different shadow volumes easier. However, there are more efficient ways to see your results.

ArcGIS Pro offers a few ways to show an area of interest for your data, including visibility ranges, definition queries, and range. To visualize your data as a dynamic range, you can use any layer, or set of layers, that contain numeric, non-date fields. Once you define the range properties for your layer, an interactive, on-screen slider is used to explore the data through a range you customized’.⁵
On the content pane, right-click on SunShadow_January1 layer and select properties. Click the Range Tab. Setting the range properties of the layer, you can explore the data interactively using a range slider.

Credit: 2016 ArcGIS
To do so, you will choose a field by clicking add range. The range can be set by any numerical field. Therefore, you cannot choose DATE_TIME as a field for range.
Click Add Range. Click the drop-down menu of Field. You will see that DATE_TIME is not in the list of fields that can be used because it is not a numerical field. You can select Azimuth. Set the extent from 120 to 236. Click Add. Click OK.

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Defining a range, you will be able to use a tool in ArcGIS Pro called Range Slider. This tool gives you the ability to filter overlapping content to make it more accessible and visible. You can see the Slider on the right side of your map.

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To set the Slider, on the top ribbon, under Map, click Range. Under Full Extent choose Sun Shadow_January1. Make sure the min and max are set to 120 and 236.

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Playback defines the speed and direction of the range on the Range Slider to move.
If you set the current range from 120 to 230. The span becomes 107. Set the number of steps to 5.
Make sure the active range is Azimuth, the same field you defined in layer properties.

Check Your Understanding

Take a look at your map. You can see the first visible range now is from 123 to 144. This azimuth range belongs to the first hour of the sunrise from 7:54 am to 9:54 am

Where is the shadow's direction of the first range? (From 7:54 am to 9:54 am)

North West
South West
North East

Click for the answer.

North West

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Click next on your slider and you can see the next result:

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This belongs to 8:35 am to 9:54 am. If you continue with the Range slider, you can see all 5 categories of time frames.
The last step shows you the changes in shadow volume and its direction towards the end of the day. The shadow moves from North West in the morning to the East towards the end of the day.

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Instead of clicking next, you can play the slider and it will play ranges after each other with the pace you have chosen. The pace, from slower to faster can be defined on the top ribbon, Range tab.

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Here is the video of how the shadows of University Park Campus buildings move from sunrise to sunset on 01/01/2021.

Video: Sun Shadow January 1 2021 (00:37) This is video is not narrated.
You have learned how to change symbology in Lesson 5. To make a more presentable animation of the shadow volumes, define the symbology of ‘SunShadow_January1’ using a gradual color change from lighter colors to darker colors. You need 5 gradual colors; for instance, you can choose a color ramp of Blue or Orange or Green or any other color you find appropriate.

Note: make sure to change the current range from 123 to 230 to see all shadow calcifications under the ‘SunShadow_January1’ layer.
Make a Screenshot of Campus with gradual symbology of SunShadow_January1. Copy and paste the screenshot into your Word document and label it Task 2.
Save your Project.

2.3 Calculate Ground Shadow Surface for Walker Building

In this section, you are going to calculate the ground surface covered by shadow during the day for Walker building.

Change the current slider range to 123-230 to see all the shadow volumes.

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Zoom to Walker building displayed in the above image.
On the Content pane, click List by Selection.

Credit: ArcGIS , 2021
Uncheck all layers. Make sure the only active (checked) layer is SunShadow_January1.
Go back to List by Drawing Order.
On the top ribbon, under the Map tab, click Select. Draw a rectangle on top of Walker building’s shadows to select them. Make sure not to select other buildings’ shadows.

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Right-click on SunShadow_January1 layer. Click Data, Export Features.

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The Export Features pane opens. Name the output feature ‘Shadows_Walker’. Click Run.
On Content Pane, uncheck ‘SunShadow_January1’.
Click symbology under Appearance and change the color to the unique value. Change the color from white to another color.

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Now you have the shadow volumes for Walker Building in Multipatch format. To convert it to Polygons, on top ribbon, click Analysis and select Tools in Geoprocessing group.
Search Multipatch Footprints. Multipatch footprints create two-dimensional polygon footprints. Click the tool.
The Input Feature Class is Shadow_Walker. Name the output ‘Shadow_Walker_footprint’. To make one unique surface, you need to group your features based on a unique field. The “Source” field which is ‘Buildings_MP_Campus’ is a unique attribute that can group or dissolve all features together based on it. Click Run.

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You can see your layer in the 2D Layers list. Uncheck Shadow Walker from the 3D Layers.

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Check Your Understanding

What is the shadow area? Do you think it is an accurate shadow area?

Click for answer.

The shadow area of Walker building is around 50682.01 square feet. It is not a correct shadow area because at the beginning of this section, we asked you to calculate the ground shadow surface. However, the result of your shadow footprint contains the building itself. Although the building’s roof is covered by shadow during certain times of the day, we are only interested in ground surface.
To solve this issue, you should subtract Walker building’s footprint from the shadow surface.
Turn off Up_Roof_Segment. Drag UP_Buildings from 3D Layers to 2D Layers and turn it on. Make sure it is on top of Shadows_Walker_footprints.

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On the top ribbon, click Analysis. Select Tools from Geoprocessing group. Search Erase.

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Your input Features will be Shadow_Walker_footprints. Erase Features will be Up_Buildings. Name the Output Feature Class ‘Shadows_Walker_final’. Click Run.
Uncheck Up_Buildings and Shadow_Walker_footprints.
Now, you will see that the building footprint is extracted from the shadow.
Turn on Up_Roof_Segments.

Credit: ChoroPhronesis Lab [4]

Check Your Understanding

What is the area of Walker building Shadow now?

Click for the answer.

35017.51 Square Feet
Uncheck Shadows_Walker_final and turn on SunShadow_January1. Clear selection if necessary.
In this section, you have learned how to calculate the ground shadow surface for Walker building. In this assignment calculate ground shadow surface for the Nursing Sciences Building.

Credit: ChoroPhronesis Lab [4]
Make a Screenshot of the ground shadow surface of Nursing Sciences Building. Copy and paste it into your Word document and label it Task 3.
Make a Screenshot attribute of ground shadow surface of Nursing Sciences Building. We are interested in the total area of shadow surface. Copy and paste it into your Word document and label it Task 4.
Save the project.